<PAGE>

                                                                EXHIBIT 10(d)(4)

                               FOURTH AMENDMENT
                                     TO THE
                         ICF KAISER INTERNATIONAL, INC.
                                RETIREMENT PLAN



          WHEREAS, the ICF Kaiser International, Inc. Retirement Plan
(hereinafter referred to as the "Plan") was established effective August 1,
1971, by ICF Kaiser International, Inc. (hereinafter referred to as the
"Company"); and

          WHEREAS, the Plan was most recently restated effective January 1,
1996; and

          WHEREAS, the restated Plan was amended subsequently on three
occasions; and

          WHEREAS, the Company desires to amend the Plan again to comply with
recent tax legislation, to reflect various administrative changes, and to
accommodate certain divestitures;

          NOW, THEREFORE, effective as of April 7, 1999, unless specifically
provided otherwise, the Plan is hereby amended in the respects hereinafter set
forth.

          1.   Section 1.7 of the Plan is hereby amended to provide as follows:

               1.7  "Closing" shall mean the consummation of a transaction in
               which the Company disposes of (i) substantially all of the assets
               used by the Company in a trade or business of the Company, or
               (ii) the Company's interest in a subsidiary.

          2.   The last sentence of the second paragraph of Section 1.10 of the
Plan is hereby deleted effective January 1, 1997.

          3.   Paragraph (e) of Section 1.13 of the Plan is hereby amended
effective January 1, 1997, to provide as follows:

                    (e)  a leased employee who pursuant to Section 414(n)(2) of
               the Code means any person (other than a person who is an employee
               without regard to this subparagraph (e)) engaged in performing
               services for a Member of a Controlled Group (the "recipient")
               pursuant to an agreement between the recipient and any other
               person ("Leasing Organization") who meets the following
               requirements:

                         (i)  he has performed services for one or more Members
                    of a Controlled Group (or for any other "related persons"
                    determined in accordance with Section 414(n)(6) of the Code)
                    on a substantially full-time basis for a period of at least
                    one year;
<PAGE>

                         (ii)  such services are under the primary direction or
                    control of the recipient; and

                         (iii) he is not participating in a "safe harbor plan"
                    of the Leasing Organization. (For this purpose a "safe
                    harbor plan" is a plan that satisfies the requirements of
                    Section 414(n)(5) of the Code, which will generally be a
                    money purchase pension plan with a nonintegrated company
                    contribution rate of at least 10% of compensation and which
                    provides for immediate participation and full and immediate
                    vesting).

          A person who is a leased employee shall also be considered an employee
          of a Member of a Controlled Group during such period (and solely for
          the purpose of determining length of service for vesting purposes, and
          shall also be considered to have been an employee for any earlier
          period in which he was a leased employee) but shall not be a
          Participant and shall not otherwise be eligible to become covered by
          the Plan during any period in which he is a leased employee.
          Notwithstanding the foregoing, the sole purpose of this Paragraph (e)
          is to define and apply the term "leased employee" strictly (and only)
          to the extent necessary to satisfy the minimum requirements of Section
          414(n) of the Code relating to "leased employees.

     4.   Section 1.16 of the Plan is hereby amended effective January 1, 1997,
to provide as follows:

          1.16 "Fund" shall mean any of the investment funds established and
          maintained in accordance with the provisions of Article VI.

     5.   Section 1.26 of the Plan is hereby amended effective January 1, 1997,
to provide as follows:

          1.26 "Non-Highly Compensated Participant" shall mean any Participant
          who is not a Highly Compensated Participant.

     6.   Section 1.43 of the Plan is hereby amended January 1, 1997, to provide
as follows:

          1.43 [Revised]

     7.   Section 2.1 of the Plan is hereby amended by the addition of a
sentence at the end thereof to provide as follows:

          Notwithstanding any other provision of the Plan to the contrary, if an
          individual is transferred directly from employment (i) with the
          Employer in a capacity other than as an Employee, or (ii) with a
          Member of a

                                       2
<PAGE>

          Controlled Group to employment with the Employer as an Employee, his
          service with the Employer or such Member of a Controlled Group shall
          be included in determining his eligibility to participate in the Plan
          pursuant to the provisions of this Section 2.1.

     8.   Section 2.6 of the Plan is hereby amended to provide as follows:

          2.6  Qualified Military Service and Compliance with Uniformed Services
               -----------------------------------------------------------------
          Employment and Reemployment Rights Act. Notwithstanding any provision
          --------------------------------------
          of the Plan to the contrary, effective as of December 12, 1994,
          contributions, benefits, and service credit with respect to Qualified
          Military Service shall be provided in accordance with Section 414(u)
          of the Code.

     9.   Article II of the Plan is hereby amended by the addition of Section
2.7 at the end thereof to provide as follows:

          2.7  Cessation of Coverage of Certain Participants. Effective as of
               ---------------------------------------------
          the date of the Closing with respect to the sale of the Environment
          and Facilities Management Group (the "EFM Group") of the Company to
          The IT Group, Inc., coverage under the Plan shall be closed to any
          individual employed by, or at a facility of, the EFM Group and
          effective as of the date of the Closing with respect to the sale of
          the stock of ICF Consulting Group, Inc. ("ICF Consulting Group") to CM
          Equity Partners, L.P., CMEP Coinvestment ICF, L.P. and various
          individuals, coverage under the Plan shall be closed to any individual
          employed by, or at a facility of, ICF Consulting Group.

     10.  Article III of the Plan is hereby amended by the addition of Section
3.7 at the end thereof to provide as follows:

          3.7  Full Vesting of Certain Participants.  Notwithstanding any other
               ------------------------------------
          provision of the Plan to the contrary, as of the date of the Closing
          with respect to the sale of the EFM Group to The IT Group, Inc., each
          Participant employed by, or at a facility of, the EFM Group shall be
          fully vested in his Account, and as of the date of the Closing with
          respect to the sale of ICF Consulting Group to CM Equity Partners,
          L.P., CMEP Coinvestment ICF, L.P. and various individuals, each
          Participant employed by, or at a facility of, ICF Consulting Group
          shall be fully vested in his Account.

                                       3
<PAGE>

     11.  The first sentence of Section 4.1 of the Plan is hereby amended by the
deletion of the phrase "or (c) dies" and the substitution of a phrase in place
thereof to provide as follows:

          "(c) dies; or (d) is terminated from employment with the Company or a
          Member of a Controlled Group due to the sale of the EFM Group or ICF
          Consulting Group,".

     12.  Section 4.4 is hereby amended effective January 1, 1998, to provide as
follows:

          4.4  Limitation on Benefits.
               ----------------------

               (a)  Incorporation of Section 415 of the Code. The provisions set
                    ----------------------------------------
          forth in this Section 4.4 are intended solely to comply with the
          requirements of Section 415 of the Code and shall be interpreted,
          applied, and if and to the extent necessary deemed modified without
          further formal language so as to satisfy solely the minimum
          requirements of said Section. For such purposes, the limitations of
          Section 415 of the Code are hereby incorporated by reference and made
          part hereof as though fully set forth herein, but shall be applied
          only to particular Plan benefits in accordance with the provisions of
          this Section 4.4, to the extent such provisions are not consistent
          with said Section 415. The limitations contained in this Section 4.4
          shall be applicable only with respect to benefits provided pursuant to
          defined contribution plans and defined benefit plans specified in
          Section 415(k) of the Code.

               (b)  Definitions.  For purposes of this Section 4.4, the
                    -----------
          following definitions shall apply in addition to those set forth in
          Article I:

                    (i)   The term "Annual Additions" shall mean the amount
               defined in Section 415 (c)(2) of the Code.

                    (ii)  The term "Annual Benefit" shall mean the benefit
               amount defined in Section 415(b)(2)(A) of the Code as adjusted
               pursuant to the provisions of Section 415(b)(2)(B), (C), (D), and
               (E) of the Code.

                    (iii) The term "Compensation" shall mean compensation as
               defined in Section 415(c)(3) of the Code.

                    (iv)  The term "Defined Benefit Fraction" for any Limitation
               Year beginning prior to January 1, 2000, shall mean the fraction
               defined in Section 415(e)(2) of the Code.

                    (v)   The term "Defined Contribution Fraction" for any
               Limitation Year beginning prior to January 1, 2000, shall mean
               the fraction defined in Section 415(e)(3) of the Code.

                                       4
<PAGE>

                    (vi)   The term "Employer" shall mean the Company and all
               Members of a Controlled Group; provided, however, that for
               purposes of applying the limitations of this Section 4.4 with
               respect to Limitation Years after December 31, 1999, "50 percent"
               rather than "80 percent" shall be used in determining Member of a
               Controlled Group defined under Section 414(b) and Section 414(c)
               of the Code.

                    (vii)  The term "Excess Amount" shall mean the excess of the
               Participant's Annual Additions for a Limitation Year over the
               Defined Contribution Maximum Permissible Amount.

                    (viii) The term "Highest Average Compensation" shall mean
               the average Compensation for the three consecutive calendar years
               during which the Participant was an active Participant in the
               Plan and had the greatest aggregate Compensation from the
               Employer.

                    (ix)   The term "Limitation Year" shall mean a calendar year
               or such other 12-month period elected by the Company pursuant to
               regulations and rulings under Section 415 of the Code.

                    (x)    The term "Defined Contribution Maximum Permissible
               Amount" shall mean Annual Additions of a Participant which do not
               exceed the lesser of (i) $30,000 (adjusted in accordance with
               regulations prescribed by the Secretary of the Treasury for
               increases in the cost of living), or (ii) 25 percent of such
               Participant's Compensation paid for such Limitation Year as set
               forth in Section 415(e)(1) of the Code. If a short Limitation
               Year is created because of an amendment changing the Limitation
               Year to a different 12-month consecutive period, such Annual
               Additions shall not exceed $30,000 multiplied by a fraction, the
               numerator of which is the number of months in the short
               Limitation Year and the denominator of which is 12.

                    (xi)   The term "Defined Benefit Maximum Permissible Amount"
               shall mean the Annual Benefit of a Participant which does not
               exceed the lesser of $90,000 or 100 percent of the Participant's
               Highest Average Compensation as set forth in Section 415(b)(1) of
               the Code.

                    (xii)  The term "Projected Annual Benefit" shall mean the
               annual retirement benefit of a Participant attributable to
               Employer contributions which would be payable to such Participant
               under a plan based on the assumptions that he continues his
               employment as a

                                       5
<PAGE>

               Participant until the Social Security Retirement Age and that his
               Compensation for the Limitation Year continues at the same rate
               until the Social Security Retirement Age, and on the basis of the
               federal Social Security Act as in effect on the last day of the
               Limitation Year. A Participant's "aggregate Projected Annual
               Retirement Benefit" shall include his Projected Annual Benefit,
               if any, under any other defined benefit plan maintained by the
               Employer.

                    (xiii) The term "Social Security Retirement Age" shall mean
               the age used as the retirement age under Section 216(l) of the
               federal Social Security Act, without regard to any age increase
               factor and as if the early retirement age under Section 216(l)(2)
               were 62.

               (c)  Limitations on Allocations Under the Plan. Notwithstanding
                    -----------------------------------------
          any other provision of the Plan to the contrary, the amount of Annual
          Additions which may be credited to the Participant's Account for any
          Limitation Year shall not exceed the lesser of the Defined
          Contribution Maximum Permissible Amount or any other limitation
          contained in the Plan. If the Annual Additions to the Account of a
          Participant in any Limitation Year would otherwise exceed such amount,
          the Excess Amount shall be disposed of by reducing the Employer
          contributions and forfeitures, if any, otherwise allocable to the
          Participant's Account for the Limitation Year. Amounts deemed to be
          forfeitures under this Paragraph (c) shall be held unallocated in a
          suspense account established for the Limitation Year and shall be
          applied against the Employer's contribution obligation for the next
          following Limitation year (and succeeding Limitation Years, as
          necessary). If a suspense account is in existence at any time during a
          Limitation Year, all amounts in the suspense account must be allocated
          to Participants' Accounts (subject to the limitations set forth in
          this Section 4.4 ) before any further Employer contributions may be
          made to the Plan on behalf of Participants. If a suspense account is
          in existence at any time during a Limitation Year pursuant to this
          Section 4.4, it will not participate in the allocation of the
          investment gains and losses on the Plan's assets.

               (d) Limitation for Multiple Defined Contribution Plan
                   -------------------------------------------------
          Participation. If a Participant is covered by any other qualified
          -------------
          defined contribution plan (whether or not terminated) maintained by
          the Employer concurrently with the Plan, and if the Annual Additions
          for the Limitation Year would otherwise exceed the amount that may be
          applied for the Participant's benefit under the limitation contained
          in Section 4.4(c), such excess shall be reduced first by returning any
          employer contributions made with respect to the Participant under an
          employee stock ownership plan, and then by returning from any such
          other plan or plans any elective employer contributions made on behalf
          of the Participant under Section

                                       6
<PAGE>

          401(k) of the Code for the Limitation Year under all such other plans
          with the income attributable thereto and any corresponding matching
          employer contributions thereto. If the limitation contained in Section
          4.4(c) is still not satisfied after the return of all such
          contributions, then the Employer contributions under this Plan shall
          be reduced as provided in Section 4.4(c).

               (e)  Limitation for Defined Benefit Plan Participation. For
                    -------------------------------------------------
          Limitation Years beginning prior to January 1, 2000, if a Participant
          in the Plan is also covered by a qualified defined benefit plan
          (whether or not terminated) maintained by the Employer, in no event
          shall the sum of the Defined Benefit Fraction and the Defined
          Contribution Fraction exceed 1.0 in any Limitation Year.

               (f)  Scope of Limitations. The limitations contained in
                    --------------------
          Paragraphs (c), (d), and (e) of this Section 4.4 shall be applicable
          only with respect to benefits provided pursuant to defined
          contribution plans and defined benefit plans described in Section
          415(k) of the Code and all such defined contribution plans (whether or
          not terminated) of the Employer shall be treated as one defined
          contribution plan and all such defined benefit plans (whether or not
          terminated) of the Employer shall be treated as one defined benefit
          plan.

     13.  Sections 4.5 and 4.6 of the Plan are hereby deleted effective January
1, 1998, in their entirety.

     14.  Article V of the Plan is hereby amended effective January 1, 1998, to
provide as follows:

                                   ARTICLE V

                              TOP-HEAVY PROVISIONS
                              --------------------


          5.1  Applicability. Notwithstanding any other provision to the
               -------------
          contrary, in the event the Plan is deemed to be a top-heavy plan for
          any Plan Year, the provisions contained in this Article V with respect
          to vesting and contributions made by the Employer shall be applicable
          with respect to such Plan Year. In the event that the Plan is
          determined to be a top-heavy plan and upon a subsequent determination
          date is determined to no longer be a top-heavy plan, the vesting and
          the contribution provisions in effect immediately preceding the Plan
          Year in which the Plan was determined to be a top-heavy plan shall
          again become applicable as of such subsequent determination date.

                                       7
<PAGE>

          5.2  Top-Heavy Definitions.  Notwithstanding the definitions set forth
               ---------------------
          in Article I, the following definitions shall be applicable to this
          Article V.

               (a)  The term "Compensation" shall have the meaning set forth in
                              ------------
          Treas. Reg. Section 1.415-2(d).

               (b)  The term "Determination Date" shall mean for any Plan Year
                              ------------------
          subsequent to the first Plan Year, the last day of the preceding Plan
          Year and for the first Plan Year of the Plan, the last day of that
          Plan Year.

               (c)  The term "Employer" shall mean the Company and all Members
                              --------
          of a Controlled Group.

               (d) The term "Key Employee" shall mean any Employee or former
                             ------------
          Employee (and the beneficiaries of such Employer) who at any time
          during the Plan Year and any of the four preceding Plan Years was an
          officer of the Employer with annual compensation greater than 50
          percent of the dollar limitation under Section 415(b)(1)(A) of the
          Code, an owner (or considered an owner) under Section 318 of the Code)
          of one of the ten largest interests in the Employer with compensation
          greater than 100 percent of the limitation under Section 415(b)(1)(A)
          of the Code, a 5 percent owner of the Employer, or a 1 percent owner
          of the Employer with annual compensation of more than $150,000.

               (e)  The term "Permissive Aggregation Group" shall mean the
                              ----------------------------
          Required Aggregation Group of plans plus any other plan or plans of
          the Employer which, when considered as a group with the Required
          Aggregation Group, would continue to satisfy the requirements of
          Section 401(a)(4) and 410 of the Code.

               (f)  The term "Present Value" shall mean for purposes of
                              -------------
          computing present value calculations in determining the Top-Heavy
          Ratio, present value calculations based on the actuarial assumptions
          as stated in the applicable plan.

               (g)  The term "Required Aggregation Group" shall mean (a) each
                              --------------------------
          tax qualified plan of the Employer in which at least one Key Employee
          participates or participated at any time during the determination
          period (regardless of whether the plan terminated), and (b) any other
          tax qualified plan of the Employer which enables a plan described in
          clause (a) to meet the requirements of Section 401(a)(4) or 410 of the
          Code.

               (h)  The term "Super Top-Heavy Group" with respect to a
                              ---------------------
          particular Plan Year shall mean a Required or Permissive Aggregation
          Group that, as of the Determination Date, would qualify as a Top-Heavy
          Group under the definition in Paragraph (j) of this Section 5.2 with
          "90

                                       8
<PAGE>

          percent" substituted for "60 percent" each place where percent"
          appears in such definition.

               (i)  The term "Super Top-Heavy Plan" with respect to a particular
                              --------------------
          Plan Year shall mean a plan that, as of the Determination Date, would
          qualify as a Top-Heavy Plan under the definition in Paragraph (k) of
          this Section 5.2 with "90 percent" substituted for "60 percent" each
          place where "60 percent" appears in such definition. A plan is also a
          "Super Top-Heavy Plan" if it is part of a Super Top-Heavy Group.

               (j)  The term "Top-Heavy Group" with respect to a particular Plan
                              ---------------
          Year shall mean a Required or Permissive Aggregation Group if the sum,
          as of the Determination Date, of the present value of the cumulative
          accrued benefits for Key Employees under all defined benefit plans
          included in such group and the aggregate of the account balances of
          Key Employees under all defined contribution plans included in such
          group exceeds 60 percent of a similar sum determined for all employees
          covered by the plans included in such group.

               (k)  The term "Top-Heavy Plan" with respect to a particular Plan
                              --------------
          Year shall mean the Plan if any of the following conditions exist:

                    (i)   If the Top-Heavy Ratio for the Plan exceeds 60 percent
               and the Plan is not part of any Required Aggregation Group or
               Permissive Aggregation Group of plans.

                    (ii)  If the Plan is a part of a Required Aggregation Group
               of plans but not part of a Permissive Aggregation Group and the
               Top-Heavy Ratio for the group of plans exceeds 60 percent.

                    (iii) If the Plan is a part of a Required Aggregation Group
               and part of a Permissive Aggregation Group of plans and the Top-
               Heavy Ratio for the Permissive Aggregation Group exceeds 60
               percent.

               (l)  The term "Top-Heavy Ratio" shall mean:
                              ---------------

                    (i)  While the Employer maintains one or more defined
               contribution plans (including any simplified employee pension
               plan) and the Employer has not maintained any defined benefit
               plan which during the 5-year period ending on the Determination
               Date has or has had accrued benefits, the Top-Heavy Ratio for the
               Plan alone or for the Required or Permissive Aggregation Group,
               as appropriate, is a fraction, the numerator of which is the sum
               of the account balances of all Key Employees as of the
               Determination Date (including any part of any account balance
               distributed in the five-year period ending

                                       9
<PAGE>

               on the Determination Date), and the denominator of which is the
               sum of all account balances (including any part of any account
               balance distributed in the five-year period ending on the
               Determination Date), both computed in accordance with Section 416
               of the Code. Both the numerator and denominator of the Top-Heavy
               Ratio are adjusted to reflect any contribution not actually made
               as of the Determination Date, but which is required to be taken
               into account on that date under Section 416 of the Code.

                    (ii)  While the Employer maintains one or more defined
               contribution plans (including any simplified employee pension
               plans) and the Employer maintains or has maintained one or more
               defined benefit plans which during the five-year period ending on
               the Determination Date has or has had any accrued benefits, the
               Top-Heavy Ratio for any Required or Permissive Aggregation Group
               as appropriate is a fraction, the numerator of which is the sum
               of account balances under the aggregated defined contribution
               plan or plans for all Key Employees, determined in accordance
               with subparagraph (i) above, and the present value of accrued
               benefits under the aggregated defined benefit plan or plans for
               all Key Employees as of the Determination Date, and the
               denominator of which is the sum of the account balances under the
               aggregated defined contribution plan or plans for all
               participants, determined in accordance with subparagraph (i)
               above, and the present value of accrued benefits under the
               defined benefit plan or plans for all participants as of the
               Determination Date, all determined in accordance with Section 416
               of the Code. The accrued benefits under a defined benefit plan in
               both the numerator and denominator of the Top-Heavy Ratio are
               adjusted for any distribution of an accrued benefit made in the
               five-year period ending on the Determination Date.

                    (iii) For purposes of subparagraphs (i) and (ii) above,
               the value of account balances and the present value of accrued
               benefits shall be determined as of the most recent valuation date
               that falls within or ends with the 12-month period ending on the
               Determination Date, except as provided in Section 416 of the Code
               for the first and second plan years of a defined benefit plan.
               The account balances and accrued benefits of a participant (1)
               who is not a Key Employee but who was a Key Employee in a prior
               year, or (2) who has not performed services for the Employer
               maintaining the Plan at any time during the 5-year period ending
               on the Determination Date will be disregarded. The calculation of
               the Top-Heavy Ratio, and the extent to which distributions,
               rollovers and transfers are taken into account will be made in
               accordance with Section 416 of the Code. Deductible employee
               contributions shall

                                       10
<PAGE>

          not be taken into account for purposes of computing the Top-Heavy
          Ratio. When aggregating plans the value of account balances and
          accrued benefits will be calculated with reference to the
          Determination Date that falls within the same calendar year.

          (m)  The term "Valuation Date" shall mean, for purposes of computing
                         --------------
     the Top-Heavy Ratio, the Determination Date.

     5.3  Top-Heavy Minimum Allocation Rules.  The following Top-Heavy Plan
          ----------------------------------
     minimum allocation rules shall apply:

          (a)  Except as otherwise provided in Paragraph (b) and (c) below, the
     Employer contributions and forfeitures allocated on behalf of any
     Participant who is not a Key Employee shall be the lesser of 3 percent of
     such Participant's Compensation or in the case where the Employer has no
     defined benefit plan which designates the Plan to satisfy Section 401 of
     the Code, the largest percentage of compensation allocated with respect to
     a Key Employee for the Plan Year. Contributions made pursuant to the
     provisions of Section 401(k) of the Code cannot be used to satisfy the
     minimum contributions for non-Key Employees under Section 416 of the Code.
     Furthermore, in making the determination of the percentage at which
     contributions are made for the Key Employee with the highest percentage,
     Contributions made pursuant to the provisions of Section 401(k) of the Code
     on behalf of Key Employees shall be taken into account.

          (b)  The provisions in paragraph (a) shall not apply to any
     Participant who is not actively employed as an Employee by the Employer on
     the last day of the Plan Year for which the minimum allocation is to be
     made.

          (c)  The provisions in Paragraph (a) shall not apply to any
     Participant to the extent the Participant is covered under any other plan
     or plans of the Employer, and by the terms of such plan or plans it is
     provided that the minimum allocation or benefit requirements applicable to
     Top-Heavy Plans shall be met in such other plan or plans. If such other
     plan is, or if one of such other plans is, a defined benefit plan
     maintained by the Employer, and such plan is a Top-Heavy Plan, the minimum
     benefit requirements applicable to Top-Heavy Plans shall be met under such
     defined benefit plan as provided therein, to the extent such benefit can be
     provided under such plan or plans. If such other plan is, or if one of such
     other plans is, a defined contribution plan maintained by the Employer, and
     such plan is a Top-Heavy Plan, the minimum allocation requirements shall be
     met under such plan, except as may be otherwise provided in such other
     plan. The application and administration of the minimum allocation or
     benefit requirements for Top-Heavy Plans shall be satisfied in a manner

                                       11
<PAGE>

     so as to only satisfy the minimum allocation/benefit requirements as
     permissible and so as to avoid any duplication of minimum
     allocation/benefits for non-Key Employees, as provided under Section 416 of
     the Code.

     5.4  Top-Heavy Vesting Schedule.  A Participant shall be entitled to the
          --------------------------
     vested interest in his Account attributable to Employer contributions
     calculated in accordance with the provisions of Article IV (or, if greater,
     in accordance with the provisions of Section 5.3) determined in accordance
     with the following schedule, if greater than under Article III:

            Years of Service            Vested Percentage
            ----------------            -----------------

            Less than 2                      0%
            2 but less than 3               20%
            3 but less than 4               40%
            4 but less than 5               60%
            5 but less than 6               80%
            6 or more                      100%

     If the Plan becomes a Top-Heavy Plan and subsequently ceases to be such,
     the vesting schedule set forth above shall continue to apply in determining
     the rights to benefits of any Participant who had at least three years of
     Service as of December 31 in the last Plan Year in which the Plan was a
     Top-Heavy Plan.  For other Participants, such schedule shall apply only to
     that portion of their Account that became vested under the vesting schedule
     set forth above as of such December 31.

     5.5  Top-Heavy Compensation Limitation.  The annual Compensation of any
          ---------------------------------
     Participant to be taken into account under the Plan during any Plan Year in
     which the Plan is determined to be a Top-Heavy Plan shall not exceed the
     limitation on Compensation set forth in Section 1.10.

     5.6  Top-Heavy Plan/Benefit Limitations.  In any Plan Year beginning prior
          ----------------------------------
     to January 1, 2000, in which the Plan is a Top-Heavy Plan, the denominators
     of the defined benefit fraction and the defined contribution fraction (as
     such terms are used in applying the benefit limitation provisions of
     Section 415 of the Code) shall be computed using 100 percent of the dollar
     limitation instead of 125 percent.

15.  Section 6.1 of the Plan is hereby amended to provide as follows:

     6.1  Directed Investment in Funds.  The Company shall cause at least three
          ----------------------------
     Funds to be established and maintained at all times.  Each such Fund shall
     be diversified and have different risk and return characteristics from the
     other Funds.  Any Fund which invests in investments with restrictions
     regarding Funds to which investment transfers may be made or to which a
     minimum investment period is applicable shall not be considered as one of

                                       12
<PAGE>

          such requisite three Funds. Each Participant, pursuant to procedures
          provided by the Trustee and accepted by the Company, upon becoming a
          Participant under the Plan, shall make an investment election
          directing the manner in which the assets of his Account (except for
          assets that have been contributed in a form other than cash and have
          not been reduced to cash), shall be invested in the Funds. The
          Accounts of Participants shall be charged or credited with their share
          net earnings, gains, losses and expenses and shall reflect the
          appreciation or depreciation, as the case may be, of the Funds. The
          Plan is intended to constitute a plan described in Section 404(c) of
          ERISA and DOL Regs. Section 2550.404c-1 and insofar as the Plan
          complies with said Section 404(c), Plan fiduciaries shall be relieved
          of liability for any losses which are the direct result of investment
          instructions given by Participants. Notwithstanding the foregoing, to
          the extent that Section 404(c) of ERISA is not applicable,
          Participants shall be named fiduciaries with respect to the investment
          of their Accounts.

     16.  The next to last sentence of Section 6.2 of the Plan is hereby amended
to provide as follows:

          "The distribution of a Participant's Account shall be made in cash or
          in shares of Company Stock, or part in each, at the election of the
          Participant, pursuant to the provisions of Article VIII."

     17.  The last sentence of Section 6.2 of the Plan is hereby amended by the
deletion of the reference to "Section 9.7" and the substitution of a reference
to "Section 9.6" in place thereof.

     18.  The first sentence of Section 7.1 of the Plan is hereby amended by the
deletion of the phrase "or (c) die" and the substitution of a phrase in place
thereof to provide as follows:

          "(c) die; or (d) terminate employment with the Company or a Member of
          a Controlled Group due to the sale of the EFM Group or ICF Consulting
          Group."

     19.  Section 8.1 of the Plan is hereby amended effective January 1, 1997,
to provide as follows:

          8.1  Distribution at Required Beginning Date. Notwithstanding any
               ---------------------------------------
          other provision of the Plan to the contrary, on and after January 1,
          1997, payment of a retired or former Participant's benefit under the
          Plan shall commence not later than the earlier of:

                    (i)  the 60th day after the end of the Plan Year in which
               the latest of the following dates occurs: (i) Participant's
               Normal Retirement Date, (ii) the tenth anniversary of the date on
               which the

                                       13
<PAGE>

               Participant first became a Participant, and (iii) the date of the
               Participant's retirement or other termination of employment; or

                    (ii)  the April 1 following the calendar year in which the
               later of the following dates occurs: (i) the date on which the
               Participant attains 70-1/2, or (ii) the date on which the
               Participant retires (except for a Participant who is a 5% owner,
               as defined in Section 416(i)(1)(B) of the Code, the date
               determined under this Paragraph (d) shall be April 1 of the
               calendar year following the calendar year in which the
               Participant attains age 70-1/2 without regard to the date of the
               Participant's retirement.

          All payments required under this Article VIII shall be determined and
          made in accordance with the regulations under Section 401(a)(9) of the
          Code, including the minimum distribution incidental benefit
          requirements of proposed Treas. Reg. (S)1.401(a)(9)-2, if applicable.
          Any non-retired Participant (other than a 5% owner) who has attained
          age 70-1/2 and who is receiving payment of his benefit while employed
          by a Member of a Controlled Group, may elect in writing in the manner,
          time, and form required by the Company to terminate payment of his
          Plan benefit otherwise payable after January 1, 1997, until after his
          retirement under the terms of the Plan in effect at such time. Any
          non-retired Participant (other than a 5% owner) who attains age 70-1/2
          in 1997 or 1998, may elect in writing in the manner, time, and form
          required by the Company to defer payment of his Plan benefit until
          after his retirement pursuant to the terms of the Plan in effect at
          such time. Notwithstanding the foregoing, the spouse of any
          Participant who so elects to terminate receiving Plan benefits which
          are being paid in a qualified joint and survivor annuity (within the
          meaning of Section 417(b) of the Code) must consent to such election
          and acknowledge the effect of the election. For purposes of Section
          417 of the Code, any recommencement of benefits under this Section 8.1
          shall be considered a new annuity starting date. If such a Participant
          does not make such an election or if the Participant is a 5% owner,
          payment of his Plan benefit shall be made or shall continue to be made
          to him pursuant to the provisions of this Section 8.1 in effect prior
          to January 1, 1997.

     20.  The first sentence of Paragraph (a) Section 8.3 of the Plan is hereby
amended to provide as follows:

               (a)  General Distribution Rule. If a Participant Retires under
                    -------------------------
          the Plan, dies, Separates from Service due to the sale of the EFM
          Group or ICF Consulting Group, or Separates from Service for any other
          reason, the entire vested balance of his Account shall be distributed
          pursuant to the provisions of this Section 8.3 and Section 8.4.

                                       14
<PAGE>

     21.  Paragraph (c) of Section 8.3 is hereby amended to provide as follows:

               (c)  Distribution in Kind. Distribution of the Vested portion of
                    --------------------
          a Participant's Account invested in Company stock shall be made in
          whole shares of Company Stock (with the value of any fractional share
          paid in cash), cash, or a combination of both, at the election of the
          Participant; provided, however, that the distribution of any cash
          payment shall be made no later than two months after the date that
          distribution of Company Stock would have occurred and shall be
          determined as of the value of Company Stock on such date of
          distribution.

     22.  Paragraph (d) of Section 8.3 of the Plan is hereby deleted.

     23.  Subparagraph (a)(v) of Section 8.4 of the Plan is hereby amended
effective January 1, 1997, to provide as follows:

               (v)  Notwithstanding any other provision of the Plan to the
          contrary, any rejection, or revocation of a rejection, of the
          automatic election of the qualified joint and survivor annuity shall
          be made only within the 90-day period prior to the Participant's
          annuity starting date. Within a reasonable period of time prior to the
          annuity starting date, the Company shall provide each Participant with
          a written explanation of (1) the terms and conditions of the qualified
          joint and survivor annuity and its financial effect on his retirement
          benefit; (2) the Participant's right to waive such joint and survivor
          annuity; (3) the rights of the Participant's spouse regarding consent
          as described above in subparagraph (ii); and (4) the right to make and
          the effect of, a revocation of an election to waive the automatic
          qualified joint and survivor annuity. Such explanation shall be
          provided at least 30 days prior to distribution unless the Participant
          (with any applicable spousal consent) waives such 30-day requirement
          and distribution commences more than 7 days after such explanation is
          provided.

     24.  Paragraph (a) of Section 8.9 of the Plan is hereby amended effective
March 17, 1997, to provide as follows:

               (a)  General. Upon proper application of a Participant in such
                    -------
          form as the Company may specify, the Company in its sole discretion
          may direct the Trustee to make a loan to the Participant. The
          application, and the resulting loan, must comply with conditions
          specified in procedures established by the Company and meet the
          following conditions:

                    (i) loans shall be made available to all parties in interest
            who are Participants or Beneficiaries on a reasonably equivalent
            basis;

                                       15
<PAGE>

               (ii)  loans shall not be made available to highly compensated
            Employees, officers, or shareholders in an amount greater then the
            amount made available to other Participants and Beneficiaries;

               (iii) loans shall bear a reasonable rate of interest;

               (iv)  loans shall be adequately secured; and

               (v)   loan documents shall provide for repayment within five
            years or over a reasonable period of time, in the case of a loan
            used to acquire any dwelling unit for use as a principal residence
            as provided under Section 72(p) of the Code.

     25.  Article IX of the Plan is hereby amended effective March 17, 1999, to
provide as follows:

                                  ARTICLE IX

                     ADMINISTRATION AND CLAIMS PROCEDURES
                     ------------------------------------


          9.1  Authority of the Company. The Company shall be the Plan
               ------------------------
          administrator for purposes of ERISA and the Code and shall have the
          authority and the power to perform the functions conferred upon it
          herein, subject to the limitations hereinafter set forth. The Company
          shall have the sole right to interpret and construe the Plan, and to
          determine any disputes arising thereunder, subject to the provisions
          of Section 9.3. In exercising such powers and authorities, the Company
          shall at all times exercise good faith, apply standards of uniform
          application, and refrain from arbitrary action. The Company may employ
          such attorneys, agents, and accountants as it may deem necessary or
          advisable to assist it in carrying out its duties hereunder. The
          Company is hereby designated as a "named fiduciary" of the Plan as
          such term is defined in Section 402(a)(2) of ERISA. The Company may
          allocate any of its responsibilities for the day-to-day operation and
          administration of the Plan to any person or persons employed by it. In
          addition, the Company, by action of its Board of Directors, may
          designate a person other than itself to carry out any of the powers,
          authorities or responsibilities which are retained by it or granted to
          it by this Article IX.

          9.2  Action of Company. Any act authorized, permitted, or required to
               -----------------
          be taken by the Company under the Plan, which has not been allocated
          or delegated in accordance with Section 9.1, may be taken by a
          majority of the members of the Board of Directors of the Company,
          either by vote at a meeting, or in writing without a meeting. All
          notices, advices, directions, certifications, approvals, and
          instructions required or authorized to be

                                       16
<PAGE>

          given by the Company under the Plan shall be in writing and signed by
          either (a) a majority of the members of the Board of Directors of the
          Company, or by such member or members as may be designated by an
          instrument in writing, signed by all the members thereof, as having
          authority to execute such documents on its behalf, or (b) a person who
          becomes authorized to act for the Company in accordance with the
          provisions of Section 9.1. Subject to the provisions of Section 9.3,
          any action taken by the Company which is authorized, permitted, or
          required under the Plan shall be final and binding upon the Company
          and the Trustee, all persons who have or who claim an interest under
          the Plan, and all third parties dealing with the Company or the
          Trustee. The Company shall have exclusive responsibility with respect
          to determining the amount of any Employer contributions. Such
          determination shall be final, binding, and conclusive upon the
          Employer, the Trustee, and all Participants, and Beneficiaries.

          9.3  Claims Review Procedure. Whenever the Company decides for
               -----------------------
          whatever reason to deny, whether in whole or in part, a claim for
          benefits filed by any person (hereinafter referred to a the
          "Claimant"), the Plan administrator shall transmit to the Claimant a
          written notice of the Company's decision, which shall be written in a
          manner calculated to be understood by the Claimant and contain a
          statement of the specific reasons for the denial of the claim and a
          restatement advising the Claimant that, within 60 days of the date on
          which he receives such notice, he may obtain review of the decision of
          the Company in accordance with the procedures hereinafter set forth.
          Within such 60-day period, the Claimant or his authorized
          representative may request that the claim denial be reviewed by filing
          with the Plan administrator a written request therefor, which request
          shall contain the following information:

               (a)  the date on which the Claimant's request was filed with the
          Plan administrator; provided, however, that the date on which the
          Claimant's request for review was in fact filed with the Plan
          administrator shall control in the event that the date of the actual
          filing is later than the date stated by the Claimant pursuant to this
          paragraph (a);

               (b)  the specific portions of the denial of his claim which the
          Claimant requests the Plan administrator to review;

               (c)  a statement by the Claimant setting forth the basis upon
          which he believes the Plan administrator should reverse the Company's
          previous denial of his claim for benefits and accept his claim as
          made; and

               (d)  any written material (offered as exhibits) which the
          Claimant desires the Plan administrator to examine in its
          consideration of his position as stated pursuant to paragraph (c).

                                       17
<PAGE>

          Within 60 days of the date determined pursuant to paragraph (a) of
          this Section 9.3, the Plan administrator shall conduct a full and fair
          review of the Company's decision denying the Claimant's claim for
          benefits. Within 60 days of the date of such hearing, the Plan
          administrator shall render its written decision on review, written in
          a manner calculated to be understood by the Claimant, specifying the
          reasons and Plan provisions upon which its decision was based.

          9.4  Indemnification. In addition to whatever rights of
               ---------------
          indemnification the members of the Board of Directors of the Company,
          or any other person or persons to whom any power, authority, or
          responsibility of the Company is allocated or delegated pursuant to
          Section 9.1, may be entitled under the articles of incorporation,
          regulations, or by-laws of the Company, under any provision of law, or
          under any other agreement, the Company shall satisfy any liability
          actually and reasonably incurred by any such person or persons,
          including expenses, attorneys' fees, judgments, fines, and amounts
          paid in settlement, in connection with any threatened, pending, or
          completed action, suit, or proceeding which is related to the exercise
          or failure to exercise by such person or persons of any of the powers,
          authority, responsibilities, or discretion provided under the Plan, or
          reasonably believed by such person or persons to be provided
          hereunder, and any action taken by such person or persons in
          connection therewith.

          9.5  Administrative Expenses.  The fees of the Trustee and all other
               -----------------------
          administrative expenses of the Plan and Trust shall be paid by the
          Trustee from the assets of the Trust unless the Company, in its
          discretion, elects to pay any such fees and/or expenses.

          9.6  Voting of Company Stock in the ICF Kaiser Stock Fund.  Each
               ----------------------------------------------------
          Participant or Beneficiary who has shares of Company Stock allocated
          to his Account shall be a named fiduciary with respect to the voting
          of Company Stock held thereunder and shall have the following powers
          and responsibilities:

               (a)  Prior to each annual or special meeting of the shareholders
          of the Company, the Company shall cause to be sent to each Participant
          and Beneficiary who has Company Stock allocated to his Account and
          invested in the ICF Kaiser Stock Fund under the Plan a copy of the
          proxy solicitation material therefor, together with a form requesting
          confidential voting instructions, with respect to the voting of such
          Company Stock as well as the voting of Company Stock for which the
          Trustee does not receive instructions. Each such Participant and/or
          Beneficiary shall instruct the Trustee to vote the number of such
          uninstructed shares of Company Stock equal to the proportion that the
          number of shares of

                                       18
<PAGE>

          Company Stock allocated to his Account and invested in the ICF Kaiser
          Stock Fund bears to the total number of shares of Company Stock in the
          Plan for which instructions are received. Upon receipt of such a
          Participant's or Beneficiary's instructions, the Trustee shall then
          vote in person, or by proxy, such shares of Company Stock as so
          instructed.

               (b)  The Company shall cause the Trustee to furnish to each
          Participant and Beneficiary who has Company Stock allocated to his
          Account and invested in the ICF Kaiser Stock Fund under the Plan
          notice of any tender or exchange offer for, or a request or invitation
          for tenders or exchanges of, Company Stock made to the Trustee. The
          Trustee shall request from each such Participant and Beneficiary
          instructions as to the tendering or exchanging of Company Stock
          allocated to his Account. Each Participant and Beneficiary who does
          not instruct the Trustee with respect to the tendering or exchanging
          of Company Stock allocated to his Account shall be deemed to have
          decided not to participate in any such tender or exchange offer. The
          Trustee shall provide Participants and Beneficiaries with a reasonable
          period of time in which they may consider any such tender or exchange
          offer for, or request or invitation for tenders or exchanges of,
          Company Stock made to the Trustee. Within the time specified by the
          Trustee, the Trustee shall tender or exchange such Company Stock as to
          which the Trustee has received instructions to tender or exchange from
          Participants and Beneficiaries.

               (c)  Instructions received from Participants and Beneficiaries by
          the Trustee regarding the voting, tendering, or exchanging of Company
          Stock shall be held in strictest confidence and shall not be divulged
          to any other person, including officers or employees of the Company,
          except as otherwise required by law, regulation or lawful process.

     26.  The first sentence of Section 10.1 of the Plan is hereby amended
effective March 17, 1999, by the deletion of the phrase "and the Committee".

     27.  The second sentence of Section 10.2 of the Plan is hereby amended
effective March 17, 1999, by the deletion of the phrase "the Committee and".

     28.  The third sentence of Section 10.3 of the Plan is hereby amended
effective March 17, 1999, by the deletion of the phrase "or Committee".

     29.  The first sentence and third sentence of Section 10.4 of the Plan are
hereby amended effective March 17, 1999, by the deletion of the phrase "and
Committee".

                                       19
<PAGE>

     30.  The term "Committee" is hereby deleted effective March 17, 1999,
throughout the Plan and the term "Company" is hereby substituted in place
thereof.


          Executed this 8/th/ day of April, 1999.

                                    ICF KAISER INTERNATIONAL, INC.



                                      By: /s/ Timothy P. O'Connor
                                          --------------------------------------

                                      And:  Senior Vice President and
                                            ------------------------------------
                                            Chief Financial Officer
                                            ------------------------------------

                                       20